During the 20th century, life expectancy in the U.S. climbed by almost 50%. That has huge implications for our finances.

If you had a daughter born in 2000, her life expectancy at birth was age 84, versus 58 for women born a century earlier, according to the Social Security Administration. If you had a son born in 2000, his life expectancy at birth was age 80, compared with 52 for men born in 1900.

Keep in mind that these life expectancies are dragged down by those who die relatively young, so they aren’t necessarily a good guide for your financial planning. Indeed, the Social Security Administration says a 65-year-old woman today can expect to live until age 87, on average, while a 65-year-old man might live until 84.

What does this mean for how we manage our money? I would focus on three key ideas.

Our time horizon is measured in decades.

When the stock market plunges, we often become fixated on our portfolio’s daily price swings and end up making panicky decisions. But provided we have a paycheck or enough cash to cover expenses in the years ahead, this obsession with short-term performance makes no sense.

Think about it: Even at age 65, we could easily live two more decades and possibly more. That is plenty of time to make money in stocks.

Consider the performance of the S&P 500 during the nine decades since 1925. The worst 20-calendar-year stretch was the two decades through 1948—and it still resulted in a 3.1% annual gain, according to Chicago investment researcher Morningstar.

In fact, if you are in your 20s or 30s, and thinking not just about yourself but also about investments you might bequeath to your children and grandchildren, your investment time horizon could be as long as 100 years. That should be plenty of time to ride out bear markets and make decent money.

One career may not be enough.

Research suggests that happiness over the course of our lives is U-shaped, with our satisfaction deteriorating through our 20s and 30s, hitting bottom in our 40s and then bouncing back from there.

What causes the decline in our happiness during our early adult years? We don’t know for sure. It might be the stress of juggling work and home life, or it could be the gradual realization that we won’t fulfill all of our youthful ambitions.

But for some, midlife dissatisfaction may reflect growing disenchantment with their chosen career. The good news: Today, thanks to our longer life expectancy, we have time for a second act.

In fact, that second act may be necessary if we are laid off. Our new career could prove more fulfilling, but it might come with a smaller paycheck.

This is a reason to start saving as soon as we enter the workforce. If we do that, we likely will have the financial flexibility to swap into a less lucrative job. What if we haven’t been good savers? We may be stuck in a job we have come to hate.

We should worry about living, not dying.

If you are early in your adult life, and you have young children but you don’t have much in savings, dying is a major financial risk, because you could leave your family in the lurch. This is why young parents should buy a heap of term life insurance.

By the time you retire, however, dying is no longer a financial risk. At that point, all your money problems would be over. Instead, the big risk is living so long that you run out of savings.

Yet many retirees manage their money as though death is imminent. Take immediate fixed annuities, which can deliver monthly income for life in return for a lump-sum payment, thereby hedging the risk that you outlive your savings.

I am not a fan of most annuities, because they are overly complicated and charge high fees. But I make an exception for immediate fixed annuities, which are a simple product with a predictable return.

You might imagine that immediate fixed annuities would be popular among income-hungry retirees. But in 2014, they had total annual sales of $9.7 billion, according to financial-services trade association Limra.

That is a 17% improvement over 2013—but it still is a pittance compared with the money gushing into mutual funds and exchange-traded funds, which hauled in $343 billion from all investors in 2014, according to the Investment Company Institute.

Similarly, retirees rush to claim Social Security early. In 2013, 49% of women applying for benefits—and 43% of men—were age 62, the youngest possible age. (This figure excludes those automatically converted over from Social Security disability benefits.)

A smart move? If you are worried about outliving your savings, it often makes sense to delay Social Security until age 66 or even age 70. That way, you can lock in a monthly check that is as much as 76% bigger, while possibly also ensuring a larger survivor benefit for your spouse.

Jonathan Clements is the author of the “Jonathan Clements Money Guide 2015.” Email: ClementsMoney@gmail.com